A HC-130 Hercules gets a brownout on a dirt airstrip.
Sea King of 845 NAS on exercise in the Jordanian desert in 2013
Downwash from a CH-47 Chinook kicks up a dust cloud resulting in brownout.

In aviation, a brownout (or brown-out) is an in-flight visibility restriction due to dust or sand in the air.[1] In a brownout, the pilot cannot see nearby objects which provide the outside visual references necessary to control the aircraft near the ground.[2] This can cause spatial disorientation and loss of situational awareness leading to an accident.[3] Pilots have compared landing during brownouts to parallel parking an automobile with one's eyes closed.[4]

Description

The brownout phenomenon causes accidents during helicopter landing and take-off operations in arid desert terrain. Intense, blinding dust clouds stirred up by the helicopter rotor downwash during near-ground flight causes significant flight safety risks from aircraft and ground obstacle collisions, and dynamic rollover due to sloped and uneven terrain.[5] Brownouts have claimed more helicopters in recent military operations than all other threats combined (as of 2005).[6]

There are several factors which affect the probability and severity of brownout:[6]

  • rotor disk loading
  • rotor configuration
  • soil composition
  • wind
  • approach speed and angle

Countermeasures to prevent brownout-related accidents include:

  • Site preparation
  • Pilot technique
  • Synthetic vision systems also known as "see and remember"[7]
  • Upgraded horizontal situation indicator with improved symbology[8]
  • Aerodynamics such as the "winged rotor" on the AgustaWestland EH101[9]
  • Non-visual displays of position and orientation data derived from suitable sensors, such as Tactile Situational Awareness Systems (TSAS) providing information to the pilot through the sense of touch using tactors.

Sensory illusions

Blowing sand and dust can cause an illusion of a tilted horizon. A pilot not using the flight instruments for reference may instinctively try to level the aircraft with respect to the false horizon, resulting in an accident. Helicopter rotor wash also causes sand to blow around outside the cockpit windows, possibly leading the pilot to experience the vection illusion, where the helicopter appears to be turning when it is actually in a level hover. This can also cause the pilot to make incorrect control inputs, which can quickly lead to disaster when hovering near the ground.[10] In night landings, aircraft lighting can enhance the visual illusions by illuminating the brownout cloud.[11]

The visible effects of sand rotor abrasion have been extensively observed in Afghanistan.[12]

U.S. military experience

Several coalition military aircraft were lost due to roll-overs while executing dust landings during the Gulf War period of 1990–91. In the decade between then and Operation Enduring Freedom, the U.S. Army recorded over 40 cases of brownout condition accidents during training at the Fort Irwin Military Reservation National Training Center in California, and other various sites. Since 1991, there have been over 230 cases of aircraft damage and/or injury due to unsuccessful take-offs or landings in a dust environment. Although the majority of the incidents occur during landings, there have been a significant number of incidents occurring during take-offs as well. For the more than 50 brown-out incidents with damage reported to date during Army military operations in the 2001–2007 time frame, 80 percent were during landings and 20 percent during takeoffs.[13]

Helicopter brownout is a US$100 million per year problem for the U.S. Military in Afghanistan and Iraq. The Army cites brownout in three out of every four helicopter accidents there.[14] Brownout accidents occur close to the ground and at low airspeed, giving these accidents a higher survivability than other types. However, there have been deaths in military accidents in Iraq and Afghanistan, and nearly all of those were preventable.[15]

An MV-22 Osprey is not visible in the large brownout dust cloud that it created during training.

Brownout accidents destroyed or severely damaged four AH-64D Apache Longbows in the first three weeks of the 2003 Iraq invasion, while only one had been lost in combat in the same time period. The tandem seat Apache has a narrower stance than the UH-60 Black Hawk, making it more susceptible to rollover if the pilot begins to lose roll attitude control from the brownout. But at night, the Apache's infra-red vision system provides improved visibility when dust obscures the moonlight — the Blackhawk's night vision goggles only amplify available visible light.[16]

The CH-47 Chinook has had a relatively high frequency of brownout accidents. As of 2007, nine Chinooks were lost in action in Afghanistan, and at least two were caused by brownout, which likely played a role in several other incidents.[17] According to the Project on Government Oversight (POGO), 12 of 41 U.S. Army brownout accidents between 2002 and 2005 involved CH-47s. Data compiled by POGO from government sources show the Chinook flew 7 percent of all U.S. Army helicopter flight hours between 2003 and 2005 but accounted for 30 percent of all brownout-related accidents.[18]

Brownout is a particular concern for the U.S. V-22 Osprey tiltrotor aircraft,[19] which was deployed for combat in Iraq in September 2007. The high proprotor disk loading creates a high-velocity downwash, which stirs up the dust cloud from a much higher altitude. This can be a problem while hovering during personnel insertion and extraction via hoist or rope.[20] Initial operational experience indicates that although the dust cloud is larger with the MV-22 than it is with the CH-46 it is replacing, pilots report regaining visibility near the ground, allowing them to use visual references prior to landing.[21]

N502MT EMS helicopter wreckage, near Pyote, Texas

Civilian

  • August 18, 2001, Vinton, California, USA — Rocky Mountain Holdings, Aerospatiale AS355F1 (N53LH) — MEDEVAC helicopter damaged in dynamic rollover after an aborted takeoff at a remote location, with no injuries. The helicopter was substantially damaged. Pilot experienced brownout after lifting off approximately 3 feet (0.91 meters) off the ground.[22]
  • September 22, 2001, Chico, California, USA — Enloe Medical Center Aerospatiale AS350BA (N911NT) — helicopter was destroyed after colliding with trees in an aborted landing at a ballpark killing the pilot and injuring one of two flight nurses on board. Witnesses on the scene reported a brownout cloud obscured their vision of the accident sequence.[23]
  • March 21, 2004, Pyote, Texas, USA — Med-Trans Bell 407 (N502MT) — EMS helicopter crashed into terrain while maneuvering in reduced visibility at night while transporting a patient. The pilot, flight paramedic, patient, and patient's mother were killed, and the flight nurse was seriously injured. Witnesses reported brown-out conditions at the time of the accident.[1]
  • June 26, 2004, Cibecue, Arizona, USA — Native American Air Ambulance AS350B3 (N5226R) — MEDEVAC helicopter landed hard on a baseball field in a brownout, damaging the tail boom, but without injuring the crew. The damage was not discovered on a post-flight inspection, or subsequent pre-flight inspections, and was only noticed by an aircraft maintenance technician 8 days later.[24]
  • August 16, 2005, Donnelly, Idaho, USA, Heliflite LLC, Hughes 369E (N500FU), helicopter was substantially damaged when the main rotor blade hit a tree on landing, with no injuries. Recent construction work at the site disturbed the surface, creating unexpected brownout conditions.[25]

Military

An AH-64A Apache from the 2nd Squadron, 6th Cavalry Regiment, leaves an enormous cloud of dust after landing at a desert airstrip in central Iraq.
  • October 19, 2001, Dalbandin, Pakistan — U.S. Army Rangers, Task Force 3/75 MH-60K Black Hawk — As the search and rescue helicopter approached to land at night, it caused a brownout, obscuring the landing area. The aircraft crashed into a sand dune, killing two rangers on board as passengers, and injuring three others.[26][27][28]
  • December 6, 2001, Forward operating base (FOB), Afghanistan — U.S. Marine Corps, HMM-365, UH-1N — Helicopter inadvertently touched down on takeoff while drifting to the right and rolled over. One member of the crew was ejected, and the other three exited before the aircraft was destroyed by fire. Another nearby helicopter was damaged by flying debris from the rotor.[29]
  • August 12, 2002, FOB, Operation Enduring Freedom — U.S. Air Force, 347th Rescue Wing, HH-60G Pave Hawk — helicopter departed slowly and had insufficient power to climb out of the dust cloud generated on take-off from its own rotor wash. The pilot tried to land and hit a sand berm. The six aircraft occupants evacuated without serious injury.[30]
  • February 13, 2003, near Ali Al Salem Air Base, Kuwait — U.S. Air Force, 20th Special Operations Squadron, MH-53M (s/n 10930) — helicopter was badly damaged when crew misjudged a night landing in brownout conditions. Some minor injuries. Aircraft was salvaged.[31]
  • March 23, 2003, U.S. Army Aviation Base Camp, Central Iraq — U.S. Army 6th Cavalry Regiment, AH-64D Apache Longbow — helicopter crashed on takeoff on the unit's first day at that base camp.[16]
  • March 28, 2003, Iraq — U.S. Army 101st Aviation Regiment, AH-64D Apache — while departing from FOB Shell for a combat mission with approximately 40 other fully loaded helicopters, the helicopter rolled over in severe brownout approximately 4 minutes after the first aircraft took off.[32][33]
  • March 28, 2003, Iraq — U.S. Army 101st Aviation Regiment, AH-64D Apache (97-5032) — after returning to FOB Shell from a combat mission, the helicopter landed hard in brownout conditions, rolled over, and was severely damaged (though later salvaged and repaired).[32][33]
  • March 31, 2003, Iraq — U.S. Army 103rd Aviation Regiment, AH-64D Apache (99-5104) creates brownout on takeoff for a MEDEVAC escort mission, resulting in main rotor strike, rollover, and loss of the aircraft.[32][34]
  • April 5, 2003, Camp Thunder Road, Kuwait — U.S. Army 101st Aviation Regiment, UH-60 Black Hawk — helicopter collided with a sling load during a pickup attempt in brownout conditions. The three injured crew members pulled the two seriously injured pilots from the burning wreckage before it was destroyed by fire.[4]
  • April 26, 2004, location not specified — U.S. Marine Corps, HMM-266, CH-46E — Hard landing during brownout. Rotor blades struck terrain, but helicopter remained upright.[35]
  • July 27, 2005, Spin Buldak Afghanistan — Royal Netherlands Air Force, 298 Squadron CH-47D Chinook (D-105) — helicopter made a "hard landing" due to "brown-out conditions" as the crew was attempting to insert forces on the border between Afghanistan and Pakistan. The aircraft was destroyed by fire but there were no injuries.[36][37]

See also

References

  1. 1 2 Special Investigation Report on Emergency Medical Services Operations (PDF). PB2006-917001. National Transportation Safety Board. June 2001. NTSB/SIR-06/01. Retrieved 2007-06-26. Brown-out conditions connote in-flight visibility restrictions due to dust or sand in the air.
  2. ↑ Key, David L. (1999-09-14). "Analysis of Army Helicopter Pilot Error Mishap Data and The Implications For Handling Qualities" (PDF). Archived from the original (PDF) on 2006-06-03. Retrieved 2007-06-23. {{cite journal}}: Cite journal requires |journal= (help)
  3. ↑ Stein, Vicki (2007-02-12). "AFOSR News – National Helicopter Experts Gather to Discuss Aerodynamic Solutions for Brownout". The Air Force Office of Scientific Research, AFRL. Archived from the original on 2014-12-03. Retrieved 2007-06-25.
  4. 1 2 Skiba, Katherine M. (2003-04-07). "U.S. helicopter crash-lands in Iraq, injuring pilots, crew". Milwaukee Journal Sentinel. Pilots have compared landing during brownouts to parallel parking a car with your eyes closed.
  5. ↑ "STO: Solicitations - Sandblaster Program". Defense Advanced Research Projects Agency. Archived from the original on 2007-05-18. Retrieved 2007-06-24.
  6. 1 2 Colby, Lt. Col. Steve (2005-03-01). "Military Spin". Rotor & Wing. Access Intelligence, LLC. Archived from the original on 2007-09-03. Retrieved 2007-06-25. Brownouts have claimed more helicopters in recent military operations than all other threats combined.
  7. ↑ "News in Brief / Kurzmeldungen". Flug Revue (Germany). Motor-Presse Stuttgart. 2007-03-18. Archived from the original on 2007-07-07.
  8. ↑ "Vertiflight Breaking News : Army Prepares Brownout Kit". AHS International. July 2004. Archived from the original on 2007-09-28. Retrieved 2007-06-28. The [multi-function display] replaces the standard horizontal situation indicator and shows the crew digital ground velocity, analog vertical velocity, digital and analog radar altimeter, and analog heading symbology.
  9. ↑ Harvey, Gareth (2005-11-28). "Super Chopper : Life-Saving Features: No More Brown-Outs". Engineering Archives. National Geographic Channel. Archived from the original on 2009-07-21. Retrieved 2009-08-01. To counteract this, the EH101's 'winged-tip' rotor blades create what its pilots call the "donut effect" – a circular window of clear air inside the dust storm that allows them to see the ground as they come in to land.
  10. ↑ Lessard, Dr. Charles (2003-04-09). "Desert sandstorms add dangers for pilots". Texas A&M Engineering. Texas A&M University. Archived from the original on 2008-05-11.
  11. ↑ Colby, Lt. Col. Steve (2005-07-01). "Military Spin". Rotor & Wing. Access Intelligence, LLC. Archived from the original on 2013-01-17. Retrieved 2007-06-25. "Pixie dust" is a strange phenomenon often encountered during night brownout landings.
  12. ↑ Yon, Michael (2009-08-17). "Kopp-Etchells Effect". Michael Yon Online. Michael Yon Online. Sometimes the halos appear like distant galaxies.
  13. ↑ Gant, Randall (April 2007). "Owning the Aviation Edge : NVGPID: A Simple Device to Train Crucial Skills" (PDF). Army Aviation. United States Army. p. 22. Archived from the original (PDF) on 2007-09-27.
  14. ↑ Sabbagh, Leslie (2006-10-03). "Flying Blind in Iraq: U.S. Helicopters Navigate Real Desert Storms". Popular Mechanics.
  15. ↑ Curry, LTC Ian P. (January 2006). "Situational Awareness and Spatial Disorientation in the Fight" (PDF). FLIGHTfax. United States Army. Retrieved 2007-06-23.
  16. 1 2 Liewer, Steve (2003-04-14). "Desert landings rattle pilots' nerves". Stars and Stripes, European edition.
  17. ↑ Goldfarb, Michael (2007-04-19). "Nobody's First Choice : Another Air Force deal that doesn't pass the smell test". The Weekly Standard.
  18. ↑ United Press International. "Rescue Helicopter has Brownout Problems". Archived from the original on 2007-09-06. Data compiled by POGO from government sources show the Chinook flew 7 percent of all U.S. Army helicopter flight hours between 2003 and 2005 but accounted for 30 percent of all brownout-related accidents.
  19. ↑ United States Department of Defense (April 2002). "V-22 Program Status Report to Congress" (PDF). Archived from the original (PDF) on 2007-09-28. {{cite journal}}: Cite journal requires |journal= (help)
  20. ↑ Wayne, Leslie (2007-04-14). "Combat, With Limits, Looms for Hybrid Aircraft". The New York Times. V-22 downdraft is so strong...that it can create "brownout" conditions...as a result, when rope ladders are used, the V-22 must hover at higher altitudes...
  21. ↑ Llinares, Rick (2006-11-11). "Interview - Major Rob Freeland, VMMT-204 - Former Operations Officer and CH-46 pilot". Dash 2 Aviation Photography. Retrieved 2007-06-23.
  22. ↑ "NTSB Accident Brief: LAX01LA283". National Transportation Safety Board. 2005-06-08. Retrieved 2007-06-26.
  23. ↑ "NTSB Accident Brief: LAX01LA304". National Transportation Safety Board. 2005-06-08. Retrieved 2007-06-26.
  24. ↑ "NTSB Accident Brief: LAX04LA285". National Transportation Safety Board. 2005-09-13. Retrieved 2007-06-26.
  25. ↑ "NTSB Accident Brief: SEA05CA173". National Transportation Safety Board. 2005-12-20. Retrieved 2007-06-26.
  26. ↑ Bahmanyar, Mir (2006). Shadow Warriors: a History of the Us Army Rangers. Reading: Osprey Publishing. p. 184. ISBN 1-84603-142-7.
  27. ↑ "Officials Report on Chinook Incidents in Afghanistan". wo Soldiers Killed; Special Forces Assault Taliban Sites. United States Department of Defense. 2001-10-20.
  28. ↑ "Dalbandin, Pakistan : 28°52'41.15"N 64°24'12.54"E". Globalsecurity.org. Retrieved 2007-06-28. The search-and-rescue Black Hawk helicopter crashed into a sand dune near the perimeter of the airfield in Dalbandin.
  29. ↑ Wilbur, Ted (2004-09-01). "Brownout.(Grampaw Pettibone)". Naval Aviation News. Vol. 86, no. 6. Naval Aviation. p. 4.
  30. ↑ Chapman, Suzann (February 2003). "Aerospace World". AIR FORCE Magazine. p. 24.
  31. ↑ "1968 USAF Serial Numbers". 2007-06-01. Archived from the original on 2007-08-08. Retrieved 2007-06-25.
  32. 1 2 3 Bernstein, Jonathan (2005). Ah-64 Apache Units of Operations Enduring Freedom and Iraqi Freedom. Oxford: Osprey Publishing (UK). pp. 53–54. ISBN 1-84176-848-0.
  33. 1 2 Chilcote, Ryan (2003-03-29). "On the Scene : First deep attack". Cable News Network. Right here on the flight line in crash landings, the helicopters landing in what are called brown-out conditions, meaning the dust on the desert floor rises up and engulfs the helicopter and it is very difficult for the pilot to see the ground in those conditions and very easy to mess up the landing.
  34. ↑ Cordesman, Anthony (2003). The Iraq War. New York: Praeger. p. 255. ISBN 0-275-98227-0.
  35. ↑ Doughty, Thomas (2004-06-22). "Corrosion repairs using the radial bristle disc.(Air Wing Toolbox)".
  36. ↑ "Officials Report on Chinook Incidents in Afghanistan". American Forces Press Service. United States Department of Defense. 2005-07-28.
  37. ↑ "Touchdown Aviation - Royal Netherlands Air Force - 298 Squadron". Archived from the original on 2007-08-16. Retrieved 2007-06-24. D-105 was lost on the 27th of July and replaced by the D-104
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